Gaining control over immune responsiveness is critical to the success of allogeneic hematopoietic cell transplantation (HCT). Immune responses of donor cells against host antigens lead to both graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL). Insufficient donor immune response against host malignant cells permits tumor cell survival. Alternatively, immune reactivity against normal host tissues can lead to fatal GVHD. Project 1 is devoted to clinical trials that are designed to manipulate post-transplant immune reactivity either to target malignant leukemia cells or to enhance regulatory T cell activity to suppress GVH. These trials extend our previous laboratory and clinical observations and are intended to help establish the role of these strategies in clinical practice. In Specific Aim 1. we will focus on the prevention of disease recurrence post-HCT in high risk populations with advanced myeloid malignancies. We have, previously demonstrated that GM-CSF based tumor vaccines in a lymphopenic milieu early after allo- HCT can safely induce GVL responses despite concurrent treatment with calcineurin inhibitors. We now plan to more rigorously test the clinical impact of this strategy by performing a prospective double blind randomized study in patients entering transplant with active disease. Induction of immune responses must be sustained in order to maintain anti-tumor surveillance. There are a number of countermeasures which can suppress these immune responses and may limit the therapeutic potency of vaccination. One such mechanism is the attenuation of T cell function by the interaction of negative regulatory molecules, such as CTLA4, with their ligands. Specific Aim 2 will focus on patients who have relapsed after allo-HCT and will investigate the safety and clinical consequences of antibody blockade of CTLA4 with ipilumumab in the post- relapse setting alone and in conjunction with GM-CSF based vaccination. Specific Aim 3 will address the flip side of immune reactivity post-HCT, namely the indiscriminate host directed consequences of chronic GVHD. Regulatory T cells (Treg) downregulate immune responses. Treg deficiency is linked to chronic GVHD. There is considerable clinical interest in restoring Treg number and activity in these patients. Low dose interleukin-2 (IL-2) delivers a proliferative signal to Treg. We have demonstrated that low doses of 1-2 can be safely administered to patients with chronic GVHD (cGVHD) and can selectively expand Treg in vivo. Initial results indicate that this strategy can induce clinically meaningful responses. We plan to formally test the clinical and immunologic response of low dose lL-2 in a phase 2 clinical study in steroid refractory cGVHD patients alone and in combination with adoptive transfer of freshly isolated donor Treg. The integrated strategy in this application will yield important new insights into the immunologic impact and relevance of GM-CSF based vaccination and the role of counter-regulatory forces mediated by Treg and molecules such as CTLA4 in tumor and host direct immune responses in humans. Dr. Ritz and I have collaborated on immune modulation transplantation for over two decades and we anticipate our partnership will continue to be extremely productive. ' RELEVANCE (See instructions): Discovering how to manipulate donor derived immune responses holds the key to improving results of allo- HCT and is the central theme of this R01 submission. The clinical trials proposed in Aims 1 and 2 and are built upon accomplishments in the past 5 years and are designed to rigorously test innovative strategies to induce and sustain anti-tumor reactivity in patients with relapsed disease or at high risk for relapse. The trials planned for Aim 3 will assess novel approaches to GVH therapy and prevention by expanding regulatory T cells in vivo. Successful modulation of immune responses will have a profound impact on outcome of transplantation and could have implications in other disease settings. PROJECT/PERFORMANGE SITE(S) (if additional space is needed, use Project/Perfonnance Site Fonnat Page)